postgresql - UTF16 十六进制转文本

Question

我有 UTF-16 十六进制表示，例如“0633064406270645”，在阿拉伯语中是“سلام”。

我想将其转换为等效的文本。在 PostgreSQL 中是否有直接的方法来做到这一点？

我可以像下面这样转换 UTF 代码点；不幸的是，似乎不支持 UTF16。关于如何在 PostgreSQL 中执行此操作的任何想法，最坏的情况我会编写一个函数？

SELECT convert_from (decode (E'D8B3D984D8A7D985', 'hex'),'UTF8');

"سلام"

SELECT convert_from (decode (E'0633064406270645', 'hex'),'UTF16');

ERROR:  invalid source encoding name "UTF16"
********** Error **********

Answer 1

PostgreSQL 本身不支持 UTF-16。我建议您在将数据提供给数据库之前将其转换为 UTF-8。如果为时已晚(错误数据已存在于您的数据库中)，您可以使用这些维护函数从 UTF-16 转换数据(从 wikipedia 复制的逻辑):

-- convert from bytea, containing UTF-16-BE data
CREATE OR REPLACE FUNCTION convert_from_utf16be(utf16_data bytea, invalid_replacement text DEFAULT '?')
  RETURNS text
  LANGUAGE sql
  IMMUTABLE
  STRICT
AS $function$
WITH source(unit) AS (
  SELECT (get_byte(utf16_data, i) << 8) | get_byte(utf16_data, i + 1)
  FROM generate_series(0, octet_length(utf16_data) - 2, 2) i
),
codes(lag, unit, lead) AS (
  SELECT lag(unit, 1) OVER (), unit, lead(unit, 1) OVER ()
  FROM source
)
SELECT string_agg(CASE
  WHEN unit >= 56320 AND unit <= 57343 THEN CASE
    WHEN lag >= 55296 AND lag <= 56319 THEN '' -- already processed
    ELSE invalid_replacement
  END
  WHEN unit >= 55296 AND unit <= 56319 THEN CASE
    WHEN lead >= 56320 AND lead <= 57343 THEN chr((unit << 10) + lead - 56613888)
    ELSE invalid_replacement
  END
  ELSE chr(unit)
END, '')
FROM codes
$function$;

-- convert from bytea, containing UTF-16-LE data
CREATE OR REPLACE FUNCTION convert_from_utf16le(utf16_data bytea, invalid_replacement text DEFAULT '?')
  RETURNS text
  LANGUAGE sql
  IMMUTABLE
  STRICT
AS $function$
WITH source(unit) AS (
  SELECT get_byte(utf16_data, i) | (get_byte(utf16_data, i + 1) << 8)
  FROM generate_series(0, octet_length(utf16_data) - 2, 2) i
),
codes(lag, unit, lead) AS (
  SELECT lag(unit, 1) OVER (), unit, lead(unit, 1) OVER ()
  FROM source
)
SELECT string_agg(CASE
  WHEN unit >= 56320 AND unit <= 57343 THEN CASE
    WHEN lag >= 55296 AND lag <= 56319 THEN '' -- already processed
    ELSE invalid_replacement
  END
  WHEN unit >= 55296 AND unit <= 56319 THEN CASE
    WHEN lead >= 56320 AND lead <= 57343 THEN chr((unit << 10) + lead - 56613888)
    ELSE invalid_replacement
  END
  ELSE chr(unit)
END, '')
FROM codes
$function$;

-- convert from bytea, containing UTF-16 data (with or without BOM)
CREATE OR REPLACE FUNCTION convert_from_utf16(utf16_data bytea, invalid_replacement text DEFAULT '?')
  RETURNS text
  LANGUAGE sql
  IMMUTABLE
  STRICT
AS $function$
SELECT CASE COALESCE(octet_length(utf16_data), 0)
  WHEN 0 THEN ''
  WHEN 1 THEN invalid_replacement
  ELSE CASE substring(utf16_data FOR 2)
    WHEN E'\\xFFFE' THEN convert_from_utf16le(substring(utf16_data FROM 3), invalid_replacement)
    ELSE convert_from_utf16be(substring(utf16_data FROM 3), invalid_replacement)
  END
END
$function$;

使用这些函数，您可以从各种 UTF-16 转换:

SELECT convert_from_utf16be(decode('0633064406270645D852DF62', 'hex')),
       convert_from_utf16le(decode('330644062706450652D862DF', 'hex')),
       convert_from_utf16(decode('FEFF0633064406270645D852DF62', 'hex')),
       convert_from_utf16(decode('FFFE330644062706450652D862DF', 'hex'));

-- convert_from_utf16be | convert_from_utf16le | convert_from_utf16 | convert_from_utf16
------------------------+----------------------+--------------------+-------------------
-- سلام𤭢                | سلام𤭢                | سلام𤭢              | سلام𤭢